Heat exchangers are used in various capacities in automotive applications. For example, all automobiles having water cooled engines employ a radiator and a heater core. Automobiles equipped with air conditioning also include an evaporator and a condenser. These heat exchangers are made from aluminum and consist of two spaced header tanks interconnected by flow tubes having cooling fins extending therefrom. Fluid is circulated through the header tanks and flow tubes to effect the necessary temperature drop.
The header tanks, flow tubes and cooling fins are rigidly attached to one another by brazing. It is has been found that this brazing operation can be most efficiently accomplished in an oven for mass production applications. The prior art teaches the use of radiant braze ovens whereby the heat exchangers are conveyed through a heated muffle tube with radiate heat energy used to raise the temperature of the heat exchangers to the braze liquification temperature.
It is has been found that the heat exchanger workparts can be more quickly and efficiently raised to the braze liquification temperature by employing the principles of convection whereby an impeller is used to convectively circulate the atmosphere within the brazing chamber through the heat exchanger workparts. Examples of prior art convection braze furnace assemblies may be had in U.S. Pat. No. 3,756,489 to Chartet, issued Sep. 4, 1973, U.S. Pat. No. 3,882,596 to Kendziora et al, issued May 13, 1975, and U.S. Pat. No. 4,501,387 to Hoyer, issued Feb. 26, 1985. These references disclose convection braze furnaces which are deficient in that the atmosphere circulated by the impellers operates to move and jostle the heat exchangers prior to and while at the braze liquification temperature whereby the resulting braze heat exchanger includes misaligned parts due to the circulating atmosphere.
Hence, according to the prior art, it is not possible to circulate the atmosphere within the braze chamber at a very high velocity for fear that the various header tanks and tube components will become misaligned prior to resolidification of the braze material. Our known attempt to overcome this problem is to support the workparts in jig fixtures while in the braze furnace. In this latter case, the jig fixture may be josseled by the momentum of the circulating convection current, but the workpart supported therein will remain in perfect alignment until braze material resolidification. The obvious drawback to this arrangement is that expensive jig fixtures must be provided and additional mass must be heated while in the furnace. Therefore, the full potential of convection brazing has not been realized and the prior art attempts to braze by convection means are only slightly more efficient than the old and well known radiant heating techniques. That is, the primary advantage of convection heating, i.e., rapid heat transfer, has been emasculated by the prior art attempts to prevent imperfect alignment of workpart components through either reduced convection current velocity or jig fixtures.